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Thread: PA-12 Weight in Tail Any Documentation?

  1. #1

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    PA-12 Weight in Tail Any Documentation?

    Recently purchased a PA-12 with very recent (7 hour) Kenmore STC installing a O320. W&B has the EWCG at 9.69. Single Pilot with lower fuel keeps it right at the bleeding edge of forward C.G.
    We are looking to add some weight to bring this a little closer to where it was prior to the upgrade at EWCG of 11.89. My IA is asking if I can show any approved data or copies of approved data on any prior PA-12's that have had weight added to the tail. Pics also welcomed.


    Thanks

    Jim

  2. #2
    behindpropellers's Avatar
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    What tailwheel is on it? Probably only need to add 1/4 of a pound or so back by the tailwheel.

    Borer prop?

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    Toss a tool bag in aft baggage. Carry a survival pack. Adjust as required for solo flight. Enjoy having capacity to carry some cargo.

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    wireweinie's Avatar
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    Add a leaf to the tail spring. Put a Bushwheel tail wheel on. Survival pack in the aft baggage (as above). Tool bag. Etc. Then think about getting a different mechanic.

    Web
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    Not sure of the prop other than it was listed in the Kenmore STC. It has the Scott 3200 tail wheel. And the comments about aft baggage are assuming it has one or that I intended to add one. At this point adding an aft baggage is not in the planning stages. We just want to get this one to fly a little more like it should without running around at the front CG edge.

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    Quote Originally Posted by Jamesandres View Post
    Not sure of the prop other than it was listed in the Kenmore STC. It has the Scott 3200 tail wheel. And the comments about aft baggage are assuming it has one or that I intended to add one. At this point adding an aft baggage is not in the planning stages. We just want to get this one to fly a little more like it should without running around at the front CG edge.
    How should it fly? Every 12 I have flown does not fly like a PA18...

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    I would suggest the instillation of the STC’d short mount Then you get the CG change you want without hauling extra weight. Very important in a 12. Keep in mind the CG moves further forward as you get lower on fuel. Also keep in mind aircraft fly slower with an aft CG. Stu

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    Eddie Foy's Avatar
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    I added weight to the tailcone of my 180. Handled it as a baggage W&B entry. Farther aft you put it, the less dead weight added to achieve the desired result.
    Last edited by Eddie Foy; 10-26-2019 at 04:42 PM.
    "Put out my hand and touched the face of God!"

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    Changing the weight/balance is a major alteration. I agree - heavier tailwheel springs might sneak by without exciting an IA.

    We had this problem with a Helio on amphibs. What a mess! I got a field approval for a 40 lb chunk of steel anchored with big bolts to the tailwheel mounting holes. Scary amount of steel! Thank God I am no longer associated with that bird.
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    moneyburner's Avatar
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    I've got a short mount (Day & Night STC). I would have to gain about 300 lbs and run with nearly no fuel to get it out of FCG. It flies okay, but always does a bit better with a passenger or some gear aft. I have a small bag of gear (gust locks, tie downs, MREs), about 15 lbs, that I keep way aft; it flies a bit slower that way. Otherwise, you need to add a bit of power to get the nose up when landing.
    Quidquid Latine dictum sit, altum videtur
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    I know some experimental guys with big motors are filling the tail post with lead shot. Using gear for ballast makes better sense than adding permanent weight.
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    So is this a paperwork exercise or are you running out of trim when you fly (you are trimming correct?). What do you carry in the plane now when you fly? Like the others have said survival gear and tool bag should be around 20-30 lbs put that behind the rear seat will help. 4 leaf tail spring is simple. the short mount is the real answer.
    DENNY
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    I has a 4# triangular block of lead in my first 12 bolted into the tailwheel area, done when then o-320 went in, I don't recall ever seeing paperwork on it. My new 12 has a lightweight starter and l/w oil cooler ny niahra, almost makes it nose light, no need for short mount and it corresponding ugly front cowling
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.
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    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by stewartb View Post
    .. Using gear for ballast makes better sense than adding permanent weight.
    yup,... go out not planning to stay, and stay a night or two.... my stepfather was not impressed with the "required" mylar space blankets that night... take good gear.... the tide got the plane, not sure if he was wet... but it got full of sand...

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    W&B is a topic I'm very immersed in. My extended airframe exp Cub REQUIRES aft ballast. Not a big deal once identified. The difficult part is getting the REQUIREMENT through the thick pilot's skull. You certificated guys have fallen asleep expecting somebody else to figure it out for you. Exp guys have to figure it out for themselves, and it isn't always easy. But a few sandbags and go figure it out!
    Last edited by stewartb; 10-26-2019 at 10:33 PM.
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    BC12D-4-85's Avatar
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    How about a small rear fuel/header tank with transfer pump? Balance loads and carry something useful on every flight. Figure out the weight needed to correct forward CG and secure a place for tank plus weight-arm. Quick fuel and vent couplings on fuel hose so easy to remove. Either have an external non-vented filler or seal the tank. Vent to main tank. Bypass (U-route) the typical electric lift pump to one of the wing tanks with a cockpit reachable flow-shutoff valve. Fill the rear tank via gravity from the main then close the U pump bypass (or external via filler). Use the fuel in flight via pump or fill and leave it for ballast when needed.

    Gary
    Last edited by BC12D-4-85; 10-27-2019 at 12:23 AM.

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    I wish there was an option for not liking a post.
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    moneyburner's Avatar
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    Quote Originally Posted by stewartb View Post
    W&B is a topic I'm very immersed in. My extended airframe exp Cub REQUIRES aft ballast. Not a big deal once identified. The difficult part is getting the REQUIREMENT through the thick pilot's skull. You certificated guys have fallen asleep expecting somebody else to figure it out for you. Exp guys have to figure it out for themselves, and it isn't always easy. But a few sandbags and go figure it out!
    Ahem. I never fell asleep concerning topics that might kill me. Math, chemistry, ballistics or physics, for example. Or my wedding.
    Quidquid Latine dictum sit, altum videtur

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    skywagon8a's Avatar
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    Quote Originally Posted by Jamesandres View Post
    Recently purchased a PA-12 with very recent (7 hour) Kenmore STC installing a O320. W&B has the EWCG at 9.69. Single Pilot with lower fuel keeps it right at the bleeding edge of forward C.G.
    We are looking to add some weight to bring this a little closer to where it was prior to the upgrade at EWCG of 11.89. My IA is asking if I can show any approved data or copies of approved data on any prior PA-12's that have had weight added to the tail. Pics also welcomed.


    Thanks

    Jim
    You have not mentioned what your empty weight is, only the CG. Both numbers are needed for the calculation. So, I picked an empty weight of 1400 as a test. Using 1400# empty 16.8 pounds of ballast will be required at the tail post area to move the empty CG back to 11.89"
    If your empty weight is 1200# only 14.4# of ballast would be required.
    What is your empty weight?

    All your mechanic needs to do is to make permanent installation of a piece of lead at the tail and fill out a 337 describing how it was done. The process is described in AC:43.13
    N1PA
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    Empty weight is 1109. Adding about 10lbs will get us back close to where it was. We both understand the requirements and use of the 337. He was just looking for prior paperwork that would make it easier for him to write up.
    If anyone has done this to their PA-12 then sharing the paperwork with another person would make it easier to write-up

    thanks

  21. #21
    gntw's Avatar
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    Quote Originally Posted by Jamesandres View Post
    Empty weight is 1109. Adding about 10lbs will get us back close to where it was. We both understand the requirements and use of the 337. He was just looking for prior paperwork that would make it easier for him to write up.
    If anyone has done this to their PA-12 then sharing the paperwork with another person would make it easier to write-up

    thanks
    have u actually weighed the plane or is it all done on paper .they tend to get heavy as they get older.every plane I weigh is always heavier then the paperwork says.

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    Bill Rusk's Avatar
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    Folks

    Putting a little survival bag in the baggage compartment does not do squat!! If you want to believe that old wives tale ....great.....I hope you believe in the tooth fairy too.

    Yes, I am trying to get your attention.

    Run the numbers. Lets say he has a 1200 pound empty weight (probably not far off for a 0-320 PA-12). To get his CG (based on the TCDS numbers).....
    1148 pds on the mains at +1 = 1148 moment
    52 pds on the tail at +200 = 10400 moment
    Total moments = 11,548 divided by weight of 1200 = 9.62 on the empty CG (pretty close to his #9.69)

    The CG range per the TCDS is 9.0 to 18.5

    So lets add 20 pounds of survival gear in the baggage compartment 20 x 56(arm) = 1120
    Moments 1148 + 1120 + 10400 = 12668 divided by new weight of 1220 = 10.38

    You moved the CG less than 1" out of a 9 inch range. I call BS. You can't feel that in the plane. If I put you in the plane and did not tell you how it was loaded I bet you a steak dinner you are not good enough to tell the difference. There are a handful of people that fly 500 hours plus in a year in the same plane, (fish spotters and patrol line guys come to mind) that might be able to feel it because they are so intimate with the plane. You are not that good. It's a placebo, and a self fulfilling prophecy.

    Someone suggested adding a quarter pound to the tail, or another leaf string. 1/4 pound will move the CG from 9.62 to 9.70. In a range of 9 to 18.5 that is totally insignificant.

    Now lets play some more (take the survival kit out)
    Airplane =1200 with 1148 on the mains and 52 on the tail gives an empty CG of 9.62 as noted above and pretty close to what his is at (I'm guessing)
    Lets add full fuel 38gal = 228pds x 23arm = 5244moment
    Pilot 200 pds x 6 arm = 1200
    1148 + 5244 + 1200 + 10,400 = 17992(arm) divided by weight 1200+228+200 = 1628 = 11.05

    So....in normal solo flight he is still in a pretty far forward CG

    Max baggage on the TCDS is 41 pounds at 56 arm. If we max out the baggage with tools and survival gear his CG goes to 12.15 By maxing out the baggage we moved the CG one inch.
    If we max out the allowable weight left, 81 pounds, and put it in the back seat, we get to 1750 (max gross) divided by 23,042(moments) = 13.16 That is as far aft as he can possibly legally load the airplane. Still not even to the half way point of the range.

    In Cubs it takes roughly 10 pounds in the tail (at the tailwheel) to move the CG one inch. In a nine inch range one inch is not all that significant. So adding 20 pounds in a baggage compartment will likely move the CG less than an inch and it just does not change the "feel" that much.

    I have removable weight in the tail of my Cub and I have played with the CG a lot. I have added up to 40 pounds of lead in the tail, and then test flown the aircraft to include multi turn spins. I am not a trained test pilot, nor am I am particularly good pilot, so take this for what it is worth. I would have to review the notes from my test flights but I can't remember much difference with 10 pounds of lead in the tail. It became noticeable when I got to 20 pounds, 30 pounds made a difference and the airplane flies great at that CG. When I hit 40 pounds it was starting to get a little lighter on the elevator than I personally liked, and I started to get auto-rotation coupling during the spins which was definitely uncomfortable.
    Even with 40 pounds in the tail I was still about 3 inches from the aft limit. I did notice that the further aft you get the CG the more noticeable it becomes. IE moving the CG one inch from 9 to 10 is not noticeable. Moving it one inch from 16 to 17 is noticeable.

    Run your own numbers and prove me wrong. A forward CG is most noticeable in the flare for a full stall 3 point. You will run out of elevator and not be able to get the tail down first. Do a bunch of full stall three points and pay attention to what is happening and how it is landing. Now put 20 pounds in your baggage compartment and go do it again and see if you can honestly tell the difference. I'll bet you can't.

    Bill

    (I am trying to get you fired up enough to really get to know your airplane. I want you to think "That Rusk guy is such a jerk.....I'm going to prove him wrong")
    Very Blessed.

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    Yes the plane was weighed after the work was completed with the Kenmore STC. I thought this was a simple question. Just looking for others that have been there done that and would be willing to share approved paperwork to help our process.

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    Bill,
    You seem to understand exactly where we are at. We have ran the numbers. As it is very simple I have a spread sheet that allows us to work up many different configurations and with 10 lbs in the tail, 41 baggage, 340 rear passenger fuel and a 99 pound pilot we still can’t get the c.g. Out the back side. Is 10 pounds enough? Yes as we would still use temp ballast in the rear seat/ baggage when solo. But with 2 average present day humans the 10 lbs gets us back a little without dragging to much extra weight around.
    Now what I was asking for was some info from someone that has used the kenmore or similar STC ( long mount) and found themselves in the same situation and added weight to the tail then completed the paperwork. With already submitted paperwork (approved data) my AI felt it would ease the process for us.

    Thanks for your understanding.
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  25. #25
    skywagon8a's Avatar
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    Quote Originally Posted by Jamesandres View Post
    My IA is asking if I can show any approved data or copies of approved data on any prior PA-12's that have had weight added to the tail. Pics also welcomed.
    Quote Originally Posted by Jamesandres View Post
    He was just looking for prior paperwork that would make it easier for him to write up.
    If anyone has done this to their PA-12 then sharing the paperwork with another person would make it easier to write-up
    Quote Originally Posted by Jamesandres View Post
    Just looking for others that have been there done that and would be willing to share approved paperwork to help our process.
    These repeated questions are indicating that you and your IA are very inexperienced. He in filling out 337s and understanding alterations. He should read 43.13 and other FAA publications.
    N1PA
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  26. #26

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    I had 22 lbs of lead bolted to the tail post of my Howard to get it to fall in the forward CG. Still carried tie downs, survival gear,spare Tailwheels tire and tube. Unless needed for range,also kept the aft fuel tank full. The airplane flew lots better loaded aft.


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  27. #27

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    I hold maybe 15 field approvals, including major brake system changes and ballast. My impression is that carrying in a field approval for another aircraft doesn't help much.

    If you have a friendly fed, just write it up on the back and get him/her to stamp block 3. Make some comment about how you fastened it, maybe with a stress/strain computation. That always impresses them.

    I still don't understand ICAs. At first they wanted all 16. Now they do not want more than a sentence - "Inspect each 100 hours for structural integrity."
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  28. #28
    SuperCub MD's Avatar
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    Guy asked a simple question... just wants to make his plane fly better and stay legal,how dare he.

    AC43.13-1B paragraph 10-22 Installation of ballast

    Everything you need to know and approved data.

    Start with figure 10-19 to calculate how much weight needed for the desired cg movement.
    Last edited by SuperCub MD; 10-27-2019 at 11:43 AM.
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  29. #29
    wireweinie's Avatar
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    Quote Originally Posted by bob turner View Post
    Changing the weight/balance is a major alteration.
    WRONG! Read Appendix A:

    (xi) Changes to the empty weight or empty balance which result in an increase in the maximum certificated weight or center of gravity limits of the aircraft.

    As this states, it's only a major if the changes result in an increase of the MAX CERTIFICATED WEIGHT or changes to the CG LIMITS. The only other way it could be a major is if you cut or welded the airframe in order to install the weight. If you clamp weights in place or replace existing bolts with longer bolts in order to secure the weight, it is a minor alteration.

    Going to a four leaf tailspring, as per a parts manual, is a minor. The fat tailwheel is an STC (337 but no further approval required), securing a survival pack doesn't even need to be listed in the logs. Plenty of ways of doing this without falling into the major category.

    If simply changing the weight and balance of the aircraft were a major, we'd be doing 337's for each and every passenger, every time we loaded cargo, or every time we gained or lost weight.

    Web
    Life's tough . . . wear a cup.

  30. #30
    BC12D-4-85's Avatar
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    Prior owner of my former PA-12-180 short mount played with CG and ballast. Plane weighed 1250 don't recall the CG but had double stacked rear baggage for placing things far aft. No lead. Finally went to enlarged elevators and rudders via STC to maintain the control he desired. I found no problems but am not a test pilot.

    Gary

  31. #31

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    To the statement that stowing gear aft isn't useful? Here's my W&B for solo flight in my 180 with Fluidyne wheel skis. Fuel load makes almost no difference.

    Click image for larger version. 

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    Add 40# in aft baggage?

    Click image for larger version. 

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    Not only does it make me legal but it makes a very noticeable change in how the plane flies.

    Same experiment in my Cub. Solo is on the assumed forward edge of the envelope.

    Click image for larger version. 

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    Add 40# aft?

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    It may not look like much but it's night and day different in control feel and cruise comfort.

    If I want to go play flying I may adda weight at the tail spring but as long as I have a 65# dog that expects to go? Problem solved.

    PS- my old short mount 160hp -12 flew better with some weight in back.


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  32. #32
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    MY -12 with CC 0-360 conversion with no added weight was 12.4” and nose heavy, ran out of trim up, nose dropped at landing. Added 8# in tail and it was 13.5” and much better but add a passenger or 42# survival items in extended baggage and now 14.7” and no need to make trim changes as i slow and add flaps to landing. Weight added in the right place is good! Almost impossible to rear CG the plane.

    I bet your plane at 9+”s will be scary nose heavy and really easy to get tail to jump up on braking. Mine was at the 12*” mark.
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  33. #33
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    Quote Originally Posted by Bill Rusk View Post
    Folks

    Putting a little survival bag in the baggage compartment does not do squat!! If you want to believe that old wives tale ....great.....I hope you believe in the tooth fairy too.

    Yes, I am trying to get your attention.

    Run the numbers. Lets say he has a 1200 pound empty weight (probably not far off for a 0-320 PA-12). To get his CG (based on the TCDS numbers).....
    1148 pds on the mains at +1 = 1148 moment
    52 pds on the tail at +200 = 10400 moment
    Total moments = 11,548 divided by weight of 1200 = 9.62 on the empty CG (pretty close to his #9.69)

    The CG range per the TCDS is 9.0 to 18.5

    So lets add 20 pounds of survival gear in the baggage compartment 20 x 56(arm) = 1120
    Moments 1148 + 1120 + 10400 = 12668 divided by new weight of 1220 = 10.38

    You moved the CG less than 1" out of a 9 inch range. I call BS. You can't feel that in the plane. If I put you in the plane and did not tell you how it was loaded I bet you a steak dinner you are not good enough to tell the difference. There are a handful of people that fly 500 hours plus in a year in the same plane, (fish spotters and patrol line guys come to mind) that might be able to feel it because they are so intimate with the plane. You are not that good. It's a placebo, and a self fulfilling prophecy.

    Someone suggested adding a quarter pound to the tail, or another leaf string. 1/4 pound will move the CG from 9.62 to 9.70. In a range of 9 to 18.5 that is totally insignificant.

    Now lets play some more (take the survival kit out)
    Airplane =1200 with 1148 on the mains and 52 on the tail gives an empty CG of 9.62 as noted above and pretty close to what his is at (I'm guessing)
    Lets add full fuel 38gal = 228pds x 23arm = 5244moment
    Pilot 200 pds x 6 arm = 1200
    1148 + 5244 + 1200 + 10,400 = 17992(arm) divided by weight 1200+228+200 = 1628 = 11.05

    So....in normal solo flight he is still in a pretty far forward CG

    Max baggage on the TCDS is 41 pounds at 56 arm. If we max out the baggage with tools and survival gear his CG goes to 12.15 By maxing out the baggage we moved the CG one inch.
    If we max out the allowable weight left, 81 pounds, and put it in the back seat, we get to 1750 (max gross) divided by 23,042(moments) = 13.16 That is as far aft as he can possibly legally load the airplane. Still not even to the half way point of the range.

    In Cubs it takes roughly 10 pounds in the tail (at the tailwheel) to move the CG one inch. In a nine inch range one inch is not all that significant. So adding 20 pounds in a baggage compartment will likely move the CG less than an inch and it just does not change the "feel" that much.

    I have removable weight in the tail of my Cub and I have played with the CG a lot. I have added up to 40 pounds of lead in the tail, and then test flown the aircraft to include multi turn spins. I am not a trained test pilot, nor am I am particularly good pilot, so take this for what it is worth. I would have to review the notes from my test flights but I can't remember much difference with 10 pounds of lead in the tail. It became noticeable when I got to 20 pounds, 30 pounds made a difference and the airplane flies great at that CG. When I hit 40 pounds it was starting to get a little lighter on the elevator than I personally liked, and I started to get auto-rotation coupling during the spins which was definitely uncomfortable.
    Even with 40 pounds in the tail I was still about 3 inches from the aft limit. I did notice that the further aft you get the CG the more noticeable it becomes. IE moving the CG one inch from 9 to 10 is not noticeable. Moving it one inch from 16 to 17 is noticeable.

    Run your own numbers and prove me wrong. A forward CG is most noticeable in the flare for a full stall 3 point. You will run out of elevator and not be able to get the tail down first. Do a bunch of full stall three points and pay attention to what is happening and how it is landing. Now put 20 pounds in your baggage compartment and go do it again and see if you can honestly tell the difference. I'll bet you can't.

    Bill

    (I am trying to get you fired up enough to really get to know your airplane. I want you to think "That Rusk guy is such a jerk.....I'm going to prove him wrong")
    I can tell a difference when I take my Abeís tie downs out of the back of the extended baggage and all my junk out from under the back seat and the seat cushions out. I canít get on my brakes like I normally can. Did that at osh stol demo and realized I couldnít get on the brakes almost at all. Iíve only had the cub stripped out like that twice for stol contests. Not much fuel and nothing in the back.


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  34. #34

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    Quote Originally Posted by RaisedByWolves View Post
    I can tell a difference when I take my Abe’s tie downs out of the back of the extended baggage and all my junk out from under the back seat and the seat cushions out. I can’t get on my brakes like I normally can. Did that at osh stol demo and realized I couldn’t get on the brakes almost at all. I’ve only had the cub stripped out like that twice for stol contests. Not much fuel and nothing in the back.


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    What brand of brake boosters are you using? I’ve run Steve’s and Cub Crafters boosters and have never felt like I’ve had enough brake on 35s and even on 31s. Used braided lines, different brake pad brands and Atlee extended gear. I’ve never felt like I was going nose over in a tail low position even with the brakes locked on landing.

  35. #35
    RaisedByWolves's Avatar
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    Quote Originally Posted by KevinJ View Post
    What brand of brake boosters are you using? Iíve run Steveís and Cub Crafters boosters and have never felt like Iíve had enough brake on 35s and even on 31s. Used braided lines, different brake pad brands and Atlee extended gear. Iíve never felt like I was going nose over in a tail low position even with the brakes locked on landing.
    Dakotaís. They are a pain to put in on a covered cub, but hey pierce can do it for you no problem. They are by far the best. Add some parking brakes while youíre at it. I never have to add fluid or mess with them. Went from the north river boosters and got sick of adding and taking fluid out. Dakotaís will lock up a 35. They are great.


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    Guess I need to try a set sometime. Never figured it was possible to lock up 35s. I guess I’ve been giving away several feet at STOL comps
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  37. #37
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    Quote Originally Posted by KevinJ View Post
    Guess I need to try a set sometime. Never figured it was possible to lock up 35s. I guess Iíve been giving away several feet at STOL comps
    Trade ya pstol flaps for brakes. Ha ha. Bring that thing out here and letís trade for a bit.


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  38. #38

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    You bet. I like to trade!

  39. #39
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    I think I'll get a boat.

    Then I can have people yell at me about free surface, metacenter, righting moments and transverse stability. "Never come about when going up river! You'll broach and capsize!"

    Nah, mate; I keep a spare Danforth in the lazarette.
    Quidquid Latine dictum sit, altum videtur
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  40. #40

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    Quote Originally Posted by reliableflyer View Post
    Also keep in mind aircraft fly slower with an aft CG. Stu
    You sure about that?

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